KEY: U = data are unavailable or less than 1 unit of measure or rounds to zero; S = data were not published because of high sampling variability or other reasons.

NOTE
Numbers may not add to totals due to rounding.

SOURCES
U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, and U.S. Department of Commerce, Census Bureau, 2007 Commodity Flow Survey, American Fact Finder, Hazardous Materials (Washington, DC: December 2009), table CF0700H02, available at http://www.census.gov/svsd/www/cfsmain.html as of December 29, 2009.